Inhibition of gene expression by anti-sense C-5 propyne oligonucleotides detected by a reporter enzyme

Using a reporter plasmid containing the luciferase gene under the control o f the insulin-like growth factor 1 (IGF-1) promoter region [including its 5 ' untranslated region (UTR)], we demonstrate that a 17-mer oligophosphoroth ioate containing C-5 propyne pyrimidines is able to inhibit luciferase gene expression in the nanomolar concentration range when the anti-sense oligon ucleotide is targeted either to a coding sequence in the luciferase gene or to the 5' UTR of the gene for IGF-1. Inhibition was obtained independently of whether the plasmid and the antisense oligonucleotide were co-transfect ed or transfected separately into hepatocarcinoma cells. However, the effic iency of inhibition by the anti-sense oligonucleotides was 10-fold greater in the first case. The unmodified oligophosphorothioate targeted to the 5' UTR of IGF-I did not inhibit luciferase gene expression at a 100-fold highe r concentration unless its length was increased from 17 to 21 nt, in which case an inhibition of gene expression was obtained and an IC50 of 200 nM wa s observed.